Method of developing a dielectric pattern on a semiconductor surface using a two-component developer

ABSTRACT

A method of developing a dielectric pattern on a semiconductor surface by using a two-component developer, each selective to a different polarity, comprising applying an electrical bias through the surface to deposit on the high dielectric areas of the pattern, a developer component which has a lower dielectric constant than the semiconductive surface to form a relatively insulating shield at the deposition areas. Then the bias polarity is reversed to deposit the other developer component on the unshielded areas, due to the higher dielectric constant at the unshielded area.

United States Patent Metcalfe et a1.

METHOD OF DEVELOPING A DIELECTRIC PATTERN ON A SEMICONDUCTOR SURFACEUSING A TWO-COMPONENT DEVELOPER Inventors: Kenneth A. Metcalfe,Lockleys;

Alwin S. Clements, Largs Bay; Clive W. Wilson, Oaklands Park, all ofAustralia The Commonwealth of Australia care of The Secretary,Department of Supply, Parkes, Canberra, Australia Filed: Oct. 2, 1972Appl. N0.: 294,001

Assignee:

US. Cl. 1l7/17.5, 96/1 S, 96/1 D,

96/1 LY, 117/37 LE Int. Cl. G03g 13/08, 003g 13/10 Field of Search117/17.5, 37 LE; 96/1 R, 96/1 8, 1 D, 1 LY; 355/10, 17; 204/181References Cited UNITED STATES PATENTS 12/1959 Epstein 117/17.5

[ Sept. 17,- 1974 3,010,842 ll/l96l Ricker 117/37 LE 3,038,799 6/1962Metcalfe et al. 96/1 R 3,078,231 2/1963 Metcalfe et al 252/621 3,081,2633/1963 Metcalfe et a1 252/621 3,527,684 9/1970 York et 117/37 LE3,563,734 2/1971 Shely 96/] R 3,589,895 6/1971 Ville 96/1 R 3,703,39911/1972 Tanaka et al. 355/10 Primary ExaminerMichael SofocleousAttorney, Agent, or FirmEric H. Waters 13 Claims, 2 Drawing Figures 7210om 0006f)! Peale/oper Pfo/Aer {Aer/mole aDeposi/ed lower Dark X/OOSGCZ lMETHOD OF DEVELOPING A DIELECTRIC PATTERN ON A SEMICONDUCTOR SURFACEUSING A TWO-COMPONENT DEVELOPER This invention relates to a method andapparatus for developing electrostatic images.

BACKGROUND OF INVENTION In developing electrostatic images it isnecessary to use marking particles which develop the field or thebackground of an electrostatic image.

It is well known that these marking particles can be in dry form or theycan be suspended in a liquid.

The marking particles must be so applied to the surface that they candeposit according to the existing latent image and this applies whetherthey are in the form of a powder cloud or held on carrier particleswhich impart a triboelectric charge to the particles, or whether theyare suspended in a liquid of high electric resistivity so that they arefreely available to deposit on the image or non-image areas.

Certain advances in the art have greatly improved the resolutionobtainable by developers, and this applies particularly to what are nowcommonly known as liquid developers, that is developer in which themarking particles are suspended in a carrier liquid having an electricalresistivity preferably in excess of ohm. centimeter and a dielectricconstant less than 3, the particles preferably being controlled byutilising a wetting medium for the particles or on the particles or amedium attached to the particles to control the particle movement.

It is also known that the behaviour of particles in insulating liquidsvary considerably according to the insulating nature of the particlesand thus for instance particles which are readily polarisable tend to godown on a surface but are then rejected when repolarisation of theparticle takes place due to contact, and it can be shown bydemonstration that insulating particles will normally have a charge in aliquid which may be inherent charge but which is retained relativelytenaciously on the particles because of the inability of the particlesto lose the charge readily, and therefore insulating particles when theyare drawn down on to a latent image area, tend to attach themselves tothe area much more permanently than particles which are conductive.

Thus it will be found that insulating particles will go down on to asurface because they are of opposite electrical sign to the surface towhich they are attracted, and they will hold to that surface as long asthe relative polarities remain on the particles and the surface, butthere will be an exchange between the particles and the surface whichwill eventually reduce the force by means of which the particles areheld to the surface, and particles can then escape from the surfaceunless held by other means.

On the other hand with more conductive particles which are more readilyable to exchange charges with a surface, a particle of one polarity,when moving down on to a surface of opposite polarity, will exchangecharges rapidly, and this tends to cause repelling of the moreconductive particles at a fairly high rate and because their polarity isthen changed, they will tend to go to an opposite polarity where exactlythe same interchange will again take place and such particles thereforetend to move alternately between areas of opposite polarity. I

Thus by selecting particles of the required dielectric constant, afairly extensive control of behaviour of developers is possible and forinstance where controlled developers are used, it is customary to use arelatively insulating medium on the surface of more conductive pigmentparticles to control the behaviour of the pig ment particles in anelectrical field, this type of developer generally being referred to ascontrolled developers, such developers achieving a higher resolution andless background contamination because of the more uniform deposition.

Another problem in connection with the art of developing electrostaticimages is that the surfaces of photoconductors which are to be madeimage containing, require first to have a charge applied to the surfacein the dark, which charge can then be modified by a light image or X-rayimage or the like, the light or X-ray or other electromagnetic wavehaving the effect of causing the photoconductive medium to becomeconductive and thus bleed away the charges from those areas, leaving animage on the remaining areas where the electromagnetic waves have notcaused the bleeding away of the charge.

It has been proposed by the applicants to effect development withoutcharging, for the reason that it is extremely difficult and costly toprovide mechanism for effecting uniform charging.

One of the greatest problems in achieving a uniform charge is that thecorona or other charging device tends to be more effective on some areasof the photoconductive surface than other, partly due to theirregularities in the surface, and partly due to lateral flow which cantake place when uneven charging results due to the somewhat erracticmovement of particles in the methods of charging adopted.

it will thus be considered that charging, while it allows a relativelyhigh voltage to be built up on insulator surface which contains aphotoconductive medium or is formed by a photoconductive medium, thishigher charge, although it can be more readily developed by markingparticles because of its magnitude, is subject to irregularities due tothe effects mentioned, and also as charge bleeding and lateral flow cantake place between the time of producing the image and the applicationof the developer, certain defects are well known to exist in any systemwhich utilises charging of an insulator surface.

SUMMARY OF INVENTION An object of the present invention is to provide animproved form of development in which charging is not resorted to, andin which photoconductive surfaces are not necessarily used, but ratheran image is produced, by modifying semiconductive surface, by patternedelectromagnetic waves and then developing the image so produced.

While it has been possible heretofore to develop such images by means ofthe more sensitive liquid developers which are now available, the imagenevertheless has lower density, and a further object of this inventiontherefore is to provide a method in which density of development can beenhanced without resorting to charging of the surface beforedevelopment.

The objects of the present invention are achieved by making use of thedifference in characteristic of a relatively insulating medium or tonerin relation to relatively more conductive toner particles, or particleshaving a different dielectric constant, that is using at least twomaterials carying in their dielectric properties, which may be theelectrical insulating liquid and the marking particles, and causing theparticles to deposit during two separate steps, comprising applying afirst and then an opposite bias to the surface containing a dielectricimage caused through exposure to electromagnetic waves or by pressure orthermal gradiants while that surface is in contact with the developer,the first bias being selected to drive down the more insulating mediumto the surface, while preventing the conducting particles from moving tothe surface. This causes the insulator to act as a control medium forfurther development in that when the more conductive substance is drivendown toward the surface by the reversed bias the substance already inposition will act as a dielectric control.

Thus for instance if a photoconductive or a semiconductor surface, whichhas been dark adapted, is subjected to a light image, or an image ofother electromagnetic waves, or a pressure or thermal image, thedielectric constant of the surface will be selectively changed in thelight struck areas to produce an image and if now a developer containinga substance of a low dielectric constant, and also toner particles whichare of higher dielectric constant, is brought into contact with themodified surface, it is possible by applying one polarity to anelectrode at or near the surface to drive down first the more insulatingmedium on to the surface which will remain on the surface on which itwas deposited, and when the surface will have an enhanced dielectricpattern on it which can be developed by the material of higherdielectric constant, that is the toner material.

In the case of chargeless images," the ultimate result to that which canbe obtained with pre-charged surfaces, excepting that where no chargehas been involved, the definition is found to be better and faults aregreatly reduced, and moreover this image is obtained in a much simplermanner because the whole of the somewhat difficult charging procedure isdispensed with.

DESCRIPTION OF DRAWINGS FIG. 1 is a diagrammatic side elevational viewof apparatus for developing a dielectric pattern on a semiconductorsurface, and

FIG. 2 shows the apparatus of FIG. 1 in a further stage of operation.

DETAILED DESCRIPTION FIG. 1 shows diagrammatically a base 1 supportingon it a membrane 2 having a semiconductor coating 3 on it. The area 4 isexposed to light while the area 5 is dark adapted, causing the area 4 tobe of higher dielectric constant (more conductive) than the area 5. Theroller 6 has a developer 7 on it which combines positive toner particles8 with a lower dielectric component 9 such as a resin.

The negative charge on the roller 6 which has an insulating coating onit locks the positive particles 8 to it but allows the lower dielectricparticles to be drawn down towards the base electrode 1 at the areaswhere the semiconductor coating has had its dielectric constant raisedto be sufficiently conductive to hold the component 9 down at this areato form an insulating shield.

At the area 5 however, the semiconductor characteristic remains and nodeposit takes place unless an excessive voltage is applied to the roller6.

FIG. 2 shows diagrammatically how when the roller 6 is again passed overthe semiconductor surface with a positive potential on it, the Tonerparticles 8 are forced off the roller when over the semiconductor area 5as a field can extend through this if the voltage is sufficient butcannot extend through the insulator layer 9 previously deposited by theroller pass of FIG. 1 and thus no toner deposit occurs here.

The voltages required and the polarity of any particular developerparticle can readily be achieved by experiment but examples are given asa guide later herein.

The invention is conveniently used with photoconductive layers on amembrane, but as said a semiconductor medium can also be used so that adifferential exists where the areas of this are varied by light exposureof X-rays or pressure or thermal effects so a differential deposition ofinsulator on the first pass exists which then increases the differentialfor the second pass.

Thus the method will be seen to increase the dielectric constantdifferential at image and non-image areas and allows intensivedeposition of developer to occurr by what can be termed an amplifieddifferential effect."

By varying voltages, as well as time and polarity, close control of boththe first and second deposition can occur.

Naturally, the medium of higher insulating value, that is lowerdielectric constant, can be a particulate substance such as a resin,co-mingled with the toner particles in an insulating liquid.

If the medium of higher insulating value is a resin or the like, and ifthe background is not to be colored in spite of deposition, mainly atthe first biasing, it should be a colorless medium, or it could be anopaque white in cases where the photoconductor base itself isdyesensitized, so as to cover the dye and give a white background.

In summing up the invention it will be realised that it consists in theuse of a first bias applied to hold the more conductive toner particlesaway from the semiconductor surface and thereby allowing the moreinsulating medium to be deposited on the exposed areas, that iselectromagnetically exposed or pressure exposed or thermally exposedareas which are then generally ofa higher dielectric effect the deposittaking place because of the control which can be exerted by themagnitude and duration of the first bias.

By controlling the second reversed bias, the toner particles can beforced down in the image areas but not where the insulator layer hasbeen deposited.

It will be realised that the invention uses differential deposition ofinsulator and less insulator particles.

EXAMPLES OF COATINGS ON A SUPPORTING MEMBRANE Coatin l Mowrtalpolyvinyl-butyral (B6OH) (Hoechst) Zinc oxide colloidal grade (DurhamChemicals) grams 350 grams The Mowital was taken up in 500 mls. acetoneand 50 mls. methyl ethyl ketone, and ball milled with the zinc oxide.

This coating can be applied to either film, metal backing or paper.

Coatin 2 lso ordosol 4501/60 short oil alkyd resin (Jordan Chemicals)Zinc oxide (colloidal grade) (Durham) Rose Bengal (sensitiser dye)Toluol 158 grams 430 grams 1200 millilitres Developer lgal) NegativeBlack Developer grams 0 moor Carbon Black 300 grams Sunflower seed oil500 grams B.P.V. oil (Viscostatic) These materials are ball milledtogether and dip coated on paper, metal, wood, or film base to form aphotoconductive layer.

THE DEVELOPERS USED COMPRISED Developer 11.

A two colour developer which was used to demonstrate the principleinvolved as it permitted blue to be deposited on the background areasit" too high voltage 10 were used during the second stage but nobackground deposit of either blue or black occurred with correctyoltage.

(More conductive) (Meggitts) (British Petrolium) 200 grams alkyd resin(1352/60) Super Beckosol (Reichold Chemicals) 0.1 parts by weight ofdeveloper 1(a) were added to one part of the following developer 1(b)and 0.1 part of developer l(c) Developer lib) Copolymeric Blue Developergrams ostaperm Blue 1330 (HA8 Insulator) (Hoechst) 200 gramsStyrene-butadiene copolymer e.g. Solprene 1205" (Phillips ImperialChemical) 100 grams Vinyl toluene-acrylate copolymer e.g. Pliolite VTACAustralian Synthetic Rubber) These materials were ball milled togetherto form a coating composition. Cobalt and zinc naphtenate driers wereadded (0.5%

and 0.5% by wt. of solid resin).

Coatin 3 lso ordosol 3501/ short oil alkyd resin (Jordan Chemicals)Titanium dioxide Toluol 430 grams 150 grams 1200 millilitres Thesematerials were ball milled together to form a coating composition.Cobalt and zinc naphthenate driers were added 45 (0.5% and 0.5% by wt.of solid resin).

Coatin 4 tyrene-5utadiene copolymer Esso polymer 200 (Buton 200) Zincoxide Lead naphthenate Cobalt naphthenate Zirconium octoate Ceriumoctoate Solvent Alsol Toluol Hexyl acetate Ethyl acetate ButanolPentoxone Disulphine Blue Acridine Orange Erythrosin B Sodiumfluorescein 6% solution in mineral spirits 6% solution in mineralspirits 6% solution in mineral spirits 6% solution in mineral spirits 1%by wt. in methyl alcohol 1% by wt. in methyl alcohol 1% by wt. in methylalcohol 150 grams 500 grams 1.0 gram 0.1 gram 1 gram 0.05 gram 900millilitres 65 millilitres 10 millilitres l0 millilitres l0 millilitres5 millilitres 2 millilitres 2 millilitres 2 millilitres 5 millilitresThe copolymeric resins were taken up in Solvesso and subsequently milledwith the blue pigment.

Lower dielectric component Developer 1(c) (Copolymeric suspension inlsopar E (Esso), and isogaraffinic hydrocarbon solvent),

lsopar 200 mls.

"Solprene 1205" 5 grams (solution of 1 gram of solid in 2 mls.)

"Pliolite VTAC" 5 grams (solution of 1 gram of solid in 2 mls.)

0.1 parts by wt.

The developer can be applied by a simple electrode or by two rollers onefollowing after the other but with opposite bias.

Time of first bias 30 volts at 30 centimetres per second.

Reverse field bias 50 volts at 10 centimetres per second.

Similar times were involved in using a bias plate having a spacing of 2millimetres from the surface being 10 developed. Additional developersfollow:

Developer 2 First pass 30 volts at 20 centimeter per second Second pass50 volts at 20 centimeter per second Developer 3 B/A/8 54 gramsHosterperm Blue B3G (Hoechst) 6l grams Solprene I205 32 grams VTAC.Dispersed in I mls. Esso I00 2000 mls. lsopar E First pass 50 volts at20 centimeter per second Second pass 10 volts at 20 centimeter persecond First pass 300 volts at 20 centimeter per second Second pass I00volts at 20 centimeter per second Developer 40 grams Permanent yellow GG(Hoechst) I0 grams Solprene I205 7 grams VTAC Dispersed in I00 mls. EssoI00 2000 mls. lsopar E First pass I00 volts at l5 centimeter per secondSecond pass 50 volts at l5 centimeter per second Exam le 6 60 gramsGraphtol Red I630 I0 grams Solprene I205 10 grams VTL CopolymerDispersed in I00 mls. Esso I00 2000 mls. Isopar E First pass 50 volts atcentimeter per second Second pass 20 volts at 20 centimeter per secondExample 7 50 grams lsol Ruby Red 30 grams Brillfast Rose Red 20 gramsPale lowering Lithographic Varnish 200 grams Rhodene alkyd resin L42/70Dispersed in I00 mls. Esso I00 2000 mls. lsopar E First pass 50 volts atIO centimeter per second Second pass 10 volts at 10 centimeter persecond Example 8 50 grams lsol Ruby Red 30 grams Brillfast Rose Red I50grams Alkyd Resin P470 l2 grams Beeswax l5 mls. Toluene dispersed in 100mls. Esso I00 2000 mls. lsopar E First pass 20 volts at 10 centimeterper second Second pass 2 volts at I0 centimeter per secondIDENTIFICATION OF TRADE MARKS AND TRADE NAMES MOWITAL B6OI-I, polyvinylbutyral resin, made by Hoechst, Germany; containing polyvinyl acetal76-78 percent, polyvinyl acetate I percent and polyvinyl alcohol 18-21percent.

ISOJORDOSOL 4501/60 short oil alkyd resin made by Jordan Chemicals BUTON200, styrene-butadiene copolymer made by Esso SOLPRENE 1205,styrene-butadiene copolymer Phillips Petroleum Corp., U.S.A., a blockcopolymer of butadiene and styrene in the ratio /25 containing 97.5percent of rubber hydrocarbon, A.S.T.M. No. I205 with majority ofstyrene molecules added as polystyrene at the end of a long chain ofbutadiene units.

SUPERBECKOSOL 1352/60, a semi-drying safflower oil isophthaIic-modifiedlong oil alkyd resin with 59-61% non-volatile matter, acid value 3-6,oil length 60%, viscosity Gardner l-loldt Y-Z.

VINYLITE VYNW, a vinyl chloride-acetate resin, approximate compositionvinyl chloride 97%, vinyl acetate 3%, and specific gravity 1.39,

PENTACITE P423 is a modified pentarethyritol ester resin with acidnumber 20-30.

PLIOLITE VT RESIN is a styrene/butadiene type copolymer rubber made bythe Goodyear Corp., U.S.A. and prepared by the G.R.S. method in whichthe butadiene polymerises in the main by a 1,4-addition. Pliolite VT isa vinyl toluene/butadiene random copolymer rubber, soluble in mineralspirits.

PLIOLITE SSD is a styrene/butadiene copolymer, KB value 60, manufacturedby Goodyear Corp., U.S.A.

PLIOLITE V.T.A.C. is a vinyl toluene/acrylate copolymer, KB value 36.

ESSO I00 Solvent is a hydrocarbon solvent supplied by Esso ChemicalsAustralia Limited, having an aromatic content of 98%, flash point of 108F., and distillation range I59-l82 C.

MICROLITH Pigments comprise a pigment and a resinous carrier. MicrolithBlack pigment contains pure neutral carbon black together with a toluenesoluble carrier resin such as Stabilite Ester 10 of the Hercules PowderCo., U.S.A.

MICROLITH BLUE 4GT comprises a stable phthalocyanine blue pigment with agreenish cast together with Stabilite Ester l resin.

MlCROLlTl-I GREEN GT comprises a medium shade of phthalocyanine greentogether with Stabilite Ester 10 resin, the microlith pigments aremanufactured by Ciba Co., Switzerland.

Colour Index of the Pigments Microlith Blue Colour Index No. 74160Microlith Green Colour Index No. 72455 ELVACITE RESIN is an acrylicresin manufactured by DuPont, Delaware, U.S.A.

Coates hydrocarbon dispersible flake black comprises pure carbon blacktogether with ethyl hydroxy cellulose resin.

B.P.V. OIL synthetic automotive lubricating oil containing antioxidantZDP," dialkyl zinc dithiophosphate in solution, made by BritishPetroleum Ltd.

KOHINOOR CARBON BLACK supplied by A. C.

Hattrick Ltd. Aust.

SUNFLOWER SEED OIL vegetable oil supplied by Meggitts Ltd., Australia.

HOSTAPERM BLUE B3G copper phthalocyanine blue, pure beta-form, made byHoechst, C.l. pigment Blue 15, Colour Index No. 74160.

GRAPHTOL BLUE BLF, phthalocyanine blue, C.I.

pigment blue made by Sandoz.

PERMANENT YELLOW 66, extra, a diazo yellow pigment without lake forminggroups, C1. pigment yellow 17, colour Index No. 21105.

BRILLFAST ROSE RED 4444, a red phosphotungsto molybolic acid toner.

ISOL RUBY RED BKS 7520 (KVK) a lithol ruby red C.I. Pigment Red 57,Agfa, Calcium lake.

PALE LOWERING LITHOGRAPHIC VARNISH a polymerized linseed oil varnishmade by Meggitts Ltd., Australia, Polylin l/S, acid value 40-65 viscosity 7.0-9.5 poises at 25 C, from alkali refined linseed oil.

RHODENE RESIN L42/70, a safflower oil modified alkyd resin made byPolymer Corporation, Australia, acid value 6-10, with 69-7l, percentsolids, 64% oil length.

ISOPAR G a hydrocarbon liquid solvent with greater than 95%isoparaffinic content, and aromatics and olifins less than 1 percent,and remainder cyclo and normal paraffins, KB No. 27, final boiling point177 C.

ISOPAR E a hydrocarbon liquid solvent with greater than 95%isoparaffinic content, aromatics and olifins less than 1 percent, withremainder cyclo and normal paraffins, KB Value 29, final boiling point143C.

B550 100 is an aromatic hydrocarbon solvent with 98% aromatics, KB value9, final boiling point 182C.

We claim:

I. The method of developing a dielectric pattern on a semiconductorsurface which is uncharged but has its dielectric constant modifiedimagewise, comprising the steps of a. subjecting the semiconductorsurface to a developer having at least a first and a second particulatedeveloper component, said components varying in their dielectricconstant and polarity, the first said developer component having adielectric constant less than the unmodified semiconductor surface, b.effecting a first development by applying an electrical bias of onepolarity selected to deposit the first said developer component to forma selective shield on the areas of high dielectric constant of thesemiconductor due to the greater general conductivity at that area, andsubsequently effecting a second development by reversing the polarity ofthe bias to deposit the second particulate developer component on theareas of the said surface where the first shielding developer has notbeen deposited and where thus the greater conductivity now exists due tothe lower conductivity of the deposited shield.

2. The method of claim I wherein the semiconductor surface is supportedon one biasing electrode and a second electrode is spaced from the saidsurface with the developer between the said surface and the said secondelectrode.

3. The method of claim I wherein the semiconductor surface is supportedon one biasing electrode and the developer is carried on an applicatorwhich is passed over the said surface in contact with the said surfaceand which forms the second electrode.

4. The method of claim 1 wherein the said developer comprises tonerparticles of a higher dielectric constant, and resin particles of alower dielectric constant.

5. The method of claim 4 wherein the said resin particles are colorless.

6. The method of claim 4 wherein the said resin particles are colored.

7. The method of claim I wherein the first biasing is relatively longerthan the second said biasing but of lower voltage.

8. The method of claim 1 wherein the semiconductor surface is aphotoconductor and the dielectric constant is varied by the applicationof electromagnetic waves.

9. The method of claim I wherein the semiconductor surface comprises aresin including therein relatively conductive particles and thedielectric constant is varied by electrical impulses.

10. The method of claim 1 wherein the semiconductor surface is adye-sensitized photoconductor of particulate form embedded in a resin,and the first said developer component is white to mask the color of thesaid photoconductor where toner particles are not deposited.

11. The method of claim 1 wherein the semiconductor surface comprises aresin including therein relatively conductive particles and thedielectric constant is varied by pressure.

12. The method of claim 1 wherein the semiconductor surface comprises aresin including therein relatively conductive particles and thedielctric constant is varied by thermal patterning.

113. The method of developing a dielectric pattern on a semiconductorsurface wherein the semiconductor surface comprises a resin includingtherein particles more conductive than the said resin, and wherein thedielectric constant is varied patternwise comprising the steps ofsupporting the said semiconductor on one electrical biasing electrodeand applying the developer by selective shield on the areas of higherdielectric constant of the semiconductor due to the greater generalconductivity at that area, and subsequently effecting a seconddevelopment by reversing the polarity of the bias to deposit the seconddeveloper component on the areas of the said surface where the firstshielding developer has not been deposited and where thus the greaterconductivity now exists due to the lower conductivity of the depositedshield on the other areas.

2. The method of claim 1 wherein the semiconductor surface is supportedon one biasing electrode and a second electrode is spaced from the saidsurface with the developer between the said surface and the said secondelectrode.
 3. The method of claim 1 wherein the semiconductor surface issupported on one biasing electrode and the developer is carried on anapplicator which is passed over the said surface in contact with thesaid surface and which forms the second electrode.
 4. The method ofclaim 1 wherein the said developer comprises toner particles of a higherdielectric constant, and rEsin particles of a lower dielectric constant.5. The method of claim 4 wherein the said resin particles are colorless.6. The method of claim 4 wherein the said resin particles are colored.7. The method of claim 1 wherein the first biasing is relatively longerthan the second said biasing but of lower voltage.
 8. The method ofclaim 1 wherein the semiconductor surface is a photoconductor and thedielectric constant is varied by the application of electromagneticwaves.
 9. The method of claim 1 wherein the semiconductor surfacecomprises a resin including therein relatively conductive particles andthe dielectric constant is varied by electrical impulses.
 10. The methodof claim 1 wherein the semiconductor surface is a dye-sensitizedphotoconductor of particulate form embedded in a resin, and the firstsaid developer component is white to mask the color of the saidphotoconductor where toner particles are not deposited.
 11. The methodof claim 1 wherein the semiconductor surface comprises a resin includingtherein relatively conductive particles and the dielectric constant isvaried by pressure.
 12. The method of claim 1 wherein the semiconductorsurface comprises a resin including therein relatively conductiveparticles and the dielctric constant is varied by thermal patterning.13. The method of developing a dielectric pattern on a semiconductorsurface wherein the semiconductor surface comprises a resin includingtherein particles more conductive than the said resin, and wherein thedielectric constant is varied patternwise comprising the steps ofsupporting the said semiconductor on one electrical biasing electrodeand applying the developer by means of an applicator which is passedover the said surface in contact with the said surface and which formsthe second electrode, a said developer having at least two developercomponents carried in an insulating liquid, said components varying intheir dielectric constant, one developer component having a dielectricconstant less than the unmodified semiconductor surface, effecting afirst development by applying a bias of one polarity selected to depositthe component of the developer with the lower dielectric constant toform a selective shield on the areas of higher dielectric constant ofthe semiconductor due to the greater general conductivity at that area,and subsequently effecting a second development by reversing thepolarity of the bias to deposit the second developer component on theareas of the said surface where the first shielding developer has notbeen deposited and where thus the greater conductivity now exists due tothe lower conductivity of the deposited shield on the other areas.